31.Either you or on of your students________to attend the meeting that is due tomorrow.
His test results are not very _____. He does well one week and badly the next.
Scientists think they have _____ in their attempt to find the causes of some major dieases.
If you ever have the _____ to go abroad to work, you should take it.
Carl wanted to play a joke on Bob but gave himself _____ by laughing.
As he had no friends and relatives in the town, the traveler tried to find a _____ somewhere.